Titanium Imido Complexes Supported by Amidinate Ligands: Synthesis, Solution Dynamics, and Solid State Structures

Article abstract of DOI:10.1021/ic9702274

Reaction of Li[PhC(NSiMe₃)₂] with the complexes [Ti(NR)Cl₂(py)₃] affords the corresponding (N,N'-bis(trimethylsilyl)benzamidinato)titanium imido derivatives [Ti(NR){PhC(NSiMe₃)₂]Cl(py)₂] [R = Bu^t (1), 2,6C₆H₃Me₂ (2), 2,6-C₆H₃Prⁱ₂ (3)], which, in solution, exist in temperature-dependent, dynamic equilibrium with their mono(pyridine) homologues [Ti(NR){PhC(NSiMe₃)₂}Cl(py)] and free pyridine. Kinetic and thermodynamic data for these processes are reported, and the relative contributions of the ΔH and ΔS terms associated with all three equilibria are identified. The arylimido complexes 2 and 3 may also be prepared by treating 1 with the appropriate arylamine. Reaction of Li[MeC(NC₆H₁₁)₂] with [Ti(NBu_t)Cl₂(py)₃] gives the binuclear N,N'-bis-(cyclohexyl)acetamidinato derivative [Ti₂(μ-NBu^t)₂{MeC₆H ₁₁)₂}₂Cl₂] (4). The X-ray structures of 2 and 4 have been determined. Crystal data for 2: triclinic, P1?, a = 11.219(5) A?. b = 12.131(6) A?, c = 13.208(7) A?, α = 80.34(5)°, β = 87,41(4)°, γ = 75.13(3)°, V = 1722.1(15) A?³, Z = 2, R = 0.054, R_w = 0.056. Crystal data for 4: triclinic, P1?, a = 10.455(3) A?, b = 10.637(5) A?, c = 11.024(3) A?, α = 90.52(4)°, β= 112.62(3)°, γ = 114.10(3)°, V= 1012.8(10) A?³, Z = 1, R = 0.0453. R_w = 0.0495.

Full text of DOI:10.1021/ic9702274

3616
Inorg. Chem. 1997, 36, 3616-3622
Titanium Imido Complexes Supported by Amidinate Ligands: Synthesis, Solution
Dynamics, and Solid State Structures
Peter J. Stewart, Alexander J. Blake, and Philip Mountford*
Department of Chemistry, University of Nottingham, Nottingham NG7 2RD, U.K.
ReceiVed February 26, 1997X
Reaction of Li[PhC(NSiMe3)2] with the complexes [Ti(NR)Cl2(py)3] affords the corresponding (N,N′-bis-
(trimethylsilyl)benzamidinato)titanium imido derivatives [Ti(NR){PhC(NSiMe3)2}Cl(py)2] [R ) But (1), 2,6-
C6H3Me2 (2), 2,6-C6H3Pri2 (3)], which, in solution, exist in temperature-dependent, dynamic equilibrium with
their mono(pyridine) homologues [Ti(NR){PhC(NSiMe3)2}Cl(py)] and free pyridine. Kinetic and thermodynamic
data for these processes are reported, and the relative contributions of the ∆H and ∆S terms associated with all
three equilibria are identified. The arylimido complexes 2 and 3 may also be prepared by treating 1 with the
appropriate arylamine. Reaction of Li[MeC(NC6H11)2] with [Ti(NBut)Cl2(py)3] gives the binuclear N,N′-bis-
(cyclohexyl)acetamidinato derivative [Ti2(µ-NBut)2{MeC(NC6H11)2}2Cl2] (4). The X-ray structures of 2 and 4
have been determined. Crystal data for 2: triclinic, P1h, a ) 11.219(5) Å, b ) 12.131(6) Å, c ) 13.208(7) Å, R
) 80.34(5)°, â ) 87.41(4)°, γ ) 75.13(3)°, V ) 1722.1(15) Å3, Z ) 2, R ) 0.054, Rw ) 0.056. Crystal data for
4: triclinic, P1h, a ) 10.455(3) Å, b ) 10.637(5) Å, c ) 11.024(3) Å, R ) 90.52(4)°, â ) 112.62(3)°, γ )
114.10(3)°, V ) 1012.8(10) Å3, Z ) 1, R ) 0.0453, Rw ) 0.0495.
Introduction
In contrast to some of these other supporting ligand sets,
amidinate ligands16,17 [having the general formula RC(NR′)2]
have been relatively little used in metal imido or oxo
chemistry.18-24 Several research groups have reported interest-
ing and novel reaction chemistry of amidinate-supported early
transition metal complexes,25-30 and we were interested in
developing synthetic routes to new amidinate complexes
containing metal-ligand multiple bonds.24 Here we describe
the synthesis and properties of some mono- and binuclear
titanium imido complexes supported by N,N′-bis(trimethysilyl)-
benzamidinato and N,N′-bis(cyclohexyl)acetamidinato ligands.31
The study of compounds containing one or more transition
metal-ligand multiple bond(s) continues to be an area of
substantial interest.1-8 The impressive variety of structural types
and, in particular, reactivity properties of such complexes is a
testament to the wide range of ancilliary ligand environments
available to support these multiply bonded functional groups.
In the course of our studies of group 4 transition metal imido
chemistry, we recently described the complexes [Ti(NR)Cl2(L)n]
(n ) 2, L ) py or 4-NC5H4But, R ) But; n ) 3, L ) py, R )
But or aryl).9-11 Simple metathesis reactions of these compexes
with neutral ligands or their anions give ready access to a wide
range of monomeric titanium imido derivatives whose ancilliary
ligand sets include the cyclopentadienyl, indenyl, and bis-
(cyclopentadienyl) fragments,12 as well as the tris(pyrazolyl)-
hydroborate13 and dibenzotetraaza[14]annulene11,14,15 η3 and η4
N-donor ligands.
Experimental Section
General Methods and Instrumentation. All manipulations were
carried out under an atmosphere of dinitrogen or argon using standard
Schlenk-line or drybox techniques. All solvents and pyridine were
(16) Barker, J.; Kilner, M. Coord. Chem. ReV 1994, 133, 219.
(17) Edelmann, F. T. Coord. Chem. ReV. 1994, 137, 403.
(18) Hagadorn, J. R.; Arnold, J. J. Am. Chem. Soc. 1996, 118, 893.
(19) Cotton, F. A.; Wojtczak, W. A. Polyhedron 1994, 13, 1337.
(20) Ribeiro da Costa, M. H.; Teuben, J. H. Personal communication cited
in ref 17.
(21) Hagadorn, J. R.; Arnold, J. Organometallics 1994, 13, 4670.
(22) Go´mez, R.; Duchateau, R.; Chernega, A. N.; Meetsma, A.; Edelmann,
F. T.; Teuben, J. H.; Green, M. L. H. J. Chem. Soc., Dalton Trans.
1995, 217.
(23) Roesky, H. W.; Meller, B.; Noltemeyer, M.; Schmidt, H.-G.; Scholz,
U.; Sheldrick, G. M. Chem. Ber. 1988, 121, 1403.
(24) Stewart, P. J.; Blake, A. J.; Mountford, P. Inorg. Chem. 1997, 36,
1982.
(25) Duchateau, R.; van Wee, C. T.; Teuben, J. H. Organometallics 1996,
15, 2291.
X Abstract published in AdVance ACS Abstracts, July 15, 1997.
(1) Nugent, W. A.; Mayer, J. M. Metal-Ligand Multiple Bonds; Wiley-
Interscience: New York, 1988.
(2) Wigley, D. E. Prog. Inorg. Chem. 1994, 42, 239.
(3) Schrock, R. R. Pure Appl. Chem. 1994, 66, 1447.
(4) Schrock, R. R. Acc. Chem. Res. 1990, 23, 158.
(5) Dehnicke, K.; Strahle, J. Angew. Chem., Int. Ed. Engl. 1992, 31, 955.
(6) Chisholm, M. H.; Rothwell, I. P. In ComprehensiVe Coordination
Chemistry; Wilkinson, G., Gillard, R. D., McCleverty, J. A., Eds.;
Pergamon Press: Oxford, U.K., 1987; Vol. 2, p 162.
(7) Bottomley, F. Polyhedron 1992, 11, 1707.
(8) Bottomley, F.; Sutin, L. AdV. Organomet. Chem. 1988, 28, 339.
(9) Blake, A. J.; Collier, P. E.; Dunn, S. C.; Li, W.-S.; Mountford, P.;
Shishkin, O. V. J. Chem. Soc., Dalton Trans. 1997, 1549.
(10) Collier, P. E.; Dunn, S. C.; Mountford, P.; Shishkin, O. V.; Swallow,
D. J. Chem. Soc., Dalton Trans. 1995, 3743.
(26) Duchateau, R.; van Wee, C. T.; Meetsma, A.; van Duijnen, P. T.;
Teuben, J. H. Organometallics 1996, 15, 2279.
(27) Vivanco, M.; Ruiz, J.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.
Organometallics 1993, 12, 1794.
(11) Dunn, S. C.; Batsanov, A. S.; Mountford, P. J. Chem. Soc., Chem.
Commun. 1994, 2007.
(12) Dunn, S. C.; Mountford, P.; Robson, D. A. J. Chem. Soc., Dalton
Trans. 1997, 293.
(28) Berno, P.; Hao, S.; Minhas, R.; Gambarotta, S. J. Am. Chem. Soc.
1994, 116, 7417.
(29) Dick, D. G.; Duchateau, R.; Edema, J. J. H.; Gambarotta, S. Inorg.
Chem. 1993, 32, 1959.
(13) Dunn, S. C.; Mountford, P.; Shishkin, O. V. Inorg. Chem. 1996, 35,
1006.
(14) Blake, A. J.; Mountford, P.; Nikonov, G. I.; Swallow, D. Chem.
Commun. 1996, 1835.
(15) Mountford, P.; Swallow, D. J. Chem. Soc., Chem. Commun. 1995,
2357.
(30) Go´mez, R.; Green, M. L. H.; Haggitt, J. L. J. Chem. Soc., Chem.
Commun. 1994, 2607.
(31) Although for ease of representation all terminal titanium-imido bonds
are drawn “TidNR”, the formal metal-ligand multiple bond order in
the complexes described herein is probably best thought of as 3
(pseudo-σ2 π4; triple bond) rather than as 2.2
S0020-1669(97)00227-9 CCC: $14.00 © 1997 American Chemical Society

Titanium Imido Complexes
Inorganic Chemistry, Vol. 36, No. 17, 1997 3617
predried over activated molecular sieves, refluxed over the appropriate
drying agent under an atmosphere of dinitrogen, and collected by
distillation. CDCl3 was dried over freshly ground calcium hydride at
room temperature, distilled under vacuum, and stored under N2 in a
Young ampule. Other reagents were used as received (Aldrich). NMR
samples were prepared in the drybox in 5 mm Wilmad tubes equipped
with a Young Teflon valve.
1H and 13C NMR spectra were recorded on a Bruker DPX 300
spectrometer. The spectra were referenced internally to residual protio
solvent (1H) or solvent (13C) resonances and are reported relative to
tetramethylsilane (δ ) 0 ppm). Chemical shifts are quoted in δ (ppm)
and coupling constants in hertz. Assignments were supported by DEPT-
135 and DEPT-90, homo- and heteronuclear, one- and two-dimensional
experiments as appropriate. IR spectra were recorded on a Nicolet
205 FTIR spectrometer in the range 4000-400 cm-1. Samples were
prepared in the drybox as Nujol mulls between CsBr plates, and data
are quoted in wavenumbers (ν, cm-1). Elemental analyses were carried
out by the analysis department of this laboratory or by Canadian
Microanalytical Service Ltd.
-0.44 (9 H, s, SiMe3). 13C{1H} NMR (CDCl3, 75.5 MHz, -40 °C):
180.3 (C6H5C), 156.5 (ipso-C6H3Me2), 150.9 (o-NC5H5), 141.7 (ipso-
C6H5), 138.5 (p-NC5H5), 133.8 (o-C6H3Me2), 128.0 (o-, m-, or p-C6H5),
127.8 (p-C6H3Me2), 126.7, 125.1 (2 × o-, m-, or p-C6H5), 123.7 (m-
NC5H5), 119.1 (m-C6H3Me2), 18.8 (C6H3Me2), 2.6, 1.2 (2 × SiMe3).
IR: 1650 (w), 1603 (s), 1589 (m), 1568 (m), 1504 (s), 1470 (vs), 1446
(vs), 1403 (s), 1295 (s), 1247 (s), 1216 (m), 1167 (w), 1152 (w), 1138
(w), 1094 (w), 1072 (m), 1042 (m), 1029 (w), 1012 (m), 1001 (m),
987 (s), 959 (s), 918 (m), 846 (vs), 786 (s), 757 (s), 699 (s), 634 (m),
587 (w), 574 (w), 508 (w), 498 (w), 436 (w) cm-1
. Anal. Calcd
(found) for C31H42ClN5Si2Ti: C, 59.7 (59.6); H, 6.8 (6.9); N, 11.2
(11.4).
NMR data for [Ti(N-2,6-C6H3Me2){PhC(NSiMe3)2}Cl(py)] (2′) are
as follows. 1H NMR (CDCl3, 300 MHz, -10 °C): 9.00 (2 H, d, J )
4.9 Hz, o-NC5H5), 7.92 (1 H, t, J ) 7.7 Hz, p-NC5H5), 7.58 (2 H,
apparent t, apparent J ) 6.4 Hz, m-NC5H5), 7.41 (3 H, s, o- and p-C6H5),
7.33 (2 H, m, m-C6H5), 6.88 (2 H, d, J ) 7.8 Hz, m-C6H3Me2), 6.62 (1
H, t, J ) 8.4 Hz, p-C6H3Me2), 2.60 (6 H, s, C6H3Me2), -0.31 (18 H,
s, SiMe3). 13C{1H} NMR (CDCl3, 75.5 MHz, 20 °C): 179.5 (C6H5C),
159.6 (ipso-C6H3Me2), 151.4 (o-NC5H5), 139.6 (p-NC5H5), 133.3 (o-
C6H3Me2), 128.8, 128.0, 126.8 (3 × o-, m-, or p-C6H5), 126.3 (p-C6H3-
Me2), 125.0 (m-NC5H5), 120.2 (m-C6H3Me2), 19.1 (C6H3Me2), 1.8
(SiMe3); the PhC(NSiMe3)2 ligand ipso carbon was not observed.
[Ti(N-2,6-C6H3Pri2){PhC(NSiMe3)2}Cl(py)2] (3). A solution of Li-
[PhC(NSiMe3)2] (0.236 g, 0.87 mmol) in THF (30 mL) was added over
10 min to a stirred solution of [Ti(N-2,6-C6H3Pri2)Cl2(py)3] (0.464 g,
0.87 mmol) in THF (20 mL) at -45 °C. The resulting solution was
allowed to warm to room temperature and then stirred for 17 h. The
volatiles were removed under reduced pressure, and the resulting orange
oil was dissolved in pentane (30 mL). After filtration, concentration,
and cooling overnight at -25 °C, orange-brown crystals of 3 formed;
these were washed with cold pentane (2 × 5 mL) and dried in Vacuo.
Yield: 0.174 g (29%).
Literature Preparations. Li[PhC(NSiMe3)2],32 Li[MeC(NC6H11)2],33
and [Ti(NR)Cl2(py)3] (R ) But, 2,6-C6H3Me2, or 2,6-C6H3Pri2)9,10 were
prepared according to literature methods.
[Ti(NBut){PhC(NSiMe3)2}Cl(py)2] (1). A solution of Li[PhC-
(NSiMe3)2] (0.693 g, 2.56 mmol) in THF (25 mL) was added over 15
min to a stirred solution of [Ti(NBut)Cl2(py)3] (1.094 g, 2.56 mmol) in
THF (30 mL) at -40 °C. The resulting solution was allowed to warm
to room temperature and then stirred for 18 h. Volatiles were removed
under reduced pressure, the resulting orange residue was dissolved in
dichloromethane, and the mixture was filtered to remove LiCl.
Evaporation of the solvent and recrystallization from hexane yielded
bright orange crystals of 1, which were washed with pentane (2 × 10
mL) and dried in Vacuo. Yield: 0.914 g (62%).
1H NMR (CDCl3, 300 MHz, -40 °C): 9.39 (4 H, d, J ) 4.7 Hz,
o-NC5H5), 7.91 (2 H, t, J ) 7.6 Hz, p-NC5H5), 7.50 (4 H, apparent t,
apparent J ) 7.0 Hz, m-NC5H5), 7.25 (3 H, m, o- and p-C6H5), 6.82 (2
H, m, m-C6H5), 0.95 (9 H, s, NBut), 0.18 (9 H, s, SiMe3), -0.49 (9 H,
s, SiMe3). 13C{1H} NMR (CDCl3, 75.5 MHz, -40 °C): 178.6 (C6H5C),
150.9 (o-NC5H5), 142.3 (ipso-C6H5), 138.0 (p-NC5H5), 127.6, 125.2,
124.8 (3 × o-, m- or p-C6H5), 123.7 (m-NC5H5), 67.8 (NCMe3), 31.0
(NCMe3), 2.4, 1.5 (2 × SiMe3). IR: 1735 (w), 1650 (w), 1603 (s),
1573 (m), 1515 (s), 1480 (s), 1468 (vs), 1454 (vs), 1445 (vs), 1245
(vs), 1215 (m), 1208 (m), 1173 (w), 1150 (w), 1134 (w), 1108 (w),
1071 (m), 1040 (m), 1030 (w), 1012 (m), 1001 (m), 983 (s), 924 (m),
842 (vs), 788 (s), 761 (s), 728 (m), 700 (s), 632 (m), 597 (w), 547 (w),
525 (w), 493 (w), 436 (w) cm-1. Anal. Calcd (found) for C27H42-
ClN5Si2Ti: C, 56.3 (55.7); H, 7.4 (7.3); N, 12.2 (11.8).
1H NMR data for [Ti(NBut){PhC(NSiMe3)2}Cl(py)] (1′) (CDCl3, 300
MHz, -15 °C): 8.96 (2 H, d, J ) 4.7 Hz, o-NC5H5), 7.98 (1 H, t, J )
7.7 Hz, p-NC5H5), 7.58 (2 H, apparent t, apparent J ) 6.7 Hz,
m-NC5H5), 7.38 (3 H, m, o- and p-C6H5), 7.31 (2 H, m, m-C6H5), 1.15
(9 H, s, NBut), -0.26 (18 H, s, SiMe3).
[Ti(N-2,6-C6H3Me2){PhC(NSiMe3)2}Cl(py)2] (2). A solution of Li-
[PhC(NSiMe3)2] (0.108 g, 0.40 mmol) in THF (15 mL) was added over
15 min to a stirred solution of [Ti(N-2,6-C6H3Me2)Cl2(py)3] (0.190 g,
0.40 mmol) in THF (15 mL) at -40 °C. The resulting solution was
allowed to warm to room temperature and then stirred for 18 h. The
volatiles were removed under reduced pressure, and the resulting orange
residue was dissolved in hexane. After filtration, concentration, and
cooling overnight at -25 °C, orange-red crystals of 2 formed; these
were washed with pentane (2 × 5 mL) and dried in Vacuo. Yield:
0.159 g (64%).
1H NMR (CDCl3, 300 MHz, -43 °C): 9.27 (4 H, d, J ) 5.1 Hz,
o-NC5H5), 7.91 (2 H, t, J ) 7.6 Hz, p-NC5H5), 7.49 (4 H, apparent t,
apparent J ) 7.0 Hz, m-NC5H5), 7.43 (1 H, m, p-C6H5), 7.33 (2 H, m,
o-C6H5), 6.99 (2 H, m, m-C6H5), 6.93 (2 H, d, J ) 7.6 Hz, m-C6H3-
Pri2), 6.74 (1 H, t, J ) 7.6 Hz, p-C6H3Pri2), 4.13 (2 H, sept, J ) 6.6
Hz, CHMe2), 0.91 (12 H, br s, CHMe2), -0.14 (9 H, s, SiMe3), -0.50
(9 H, s, SiMe3). 13C{1H} NMR (CDCl3, 75.5 MHz, -43 °C): 180.1
(C6H5C), 153.0 (ipso-C6H3Pri2), 150.5 (o-NC5H5), 145.1 (o-C6H3Pri2)
141.9 (ipso-C6H5), 138.4 (p-NC5H5), 128.2 (o-, m-, or p-C6H5), 127.9
(p-C6H3Pri2), 125.1 (o-, m-, or p-C6H5), 124.1 (m-NC5H5), 122.5 (o-,
m-, or p-C6H5), 120.0 (m-C6H3Pri2), 27.1 (CHMe2), 24.5 (CHMe2), 2.6,
0.8 (2 × SiMe3). IR: 1590 (w), 1570 (w), 1504 (w), 1249 (m), 1137
(w), 1071 (w), 1042 (w), 922 (m), 844 (s), 754 (m). 743 (m), 722
(m), 700 (m), 633 (w), 516 (w), 461 (w), 404 (w). Anal. Calcd (found)
for C35H50ClN5Si2Ti: C, 61.8 (61.0); H, 7.4 (7.6); N, 10.3 (9.9).
NMR data for [Ti(N-2,6-C6H3Pri2){PhC(NSiMe3)2}Cl(py)] (3′) are
as follows. 1H NMR (CDCl3, 300 MHz, 25 °C): 8.98 (2 H, d, J ) 4.8
Hz, o-NC5H5), 7.98 (1 H, t, J ) 7.6 Hz, p-NC5H5), 7.57 (2 H, apparent
t, apparent J ) 7.0 Hz, m-NC5H5), 7.41 (2 H, m, o-C6H5), 7.30 (3 H,
m, m- and p-C6H5), 6.94 (2 H, d, J ) 7.6 Hz, m-C6H3Pri2), 6.79 (1 H,
m, p-C6H3Pri2), 4.38 (2 H, sept, J ) 6.8 Hz, CHMe2), 1.31 (6 H, d, J
) 6.6 Hz, CHMe2), 1.28 (6 H, d, J ) 6.7 Hz, CHMe2), -0.27 (18 H,
s, SiMe3). 13C{1H} NMR (CDCl3, 75.5 MHz, 25 °C): 179.8 (C6H5C),
157.2 (ipso-C6H3Pri2), 151.4 (o-NC5H5), 143.7 (o-C6H3Pri2), 139.8 (p-
NC5H5), 135.9 (ipso-C6H5), 128.9 (o-, m-, or p-C6H5), 128.1 (p-C6H3-
Pri2), 126.7, 125.1 (2 × o-, m-, or p-C6H5), 123.7 (m-NC5H5), 121.8
(m-C6H3Pri2), 27.7 (CHMe2), 24.3, 23.7 (2 × CHMe2), 1.8 (SiMe3).
NMR-Scale Reaction of [Ti(NBut){PhC(NSiMe3)2}Cl(py)2] (1)
with 2,6-Dimethylaniline. A solution of 1 (9.0 mg, 0.016 mmol) in
CDCl3 (0.6 mL) in a 5 mm NMR tube was treated with ca. 1.5 equiv
1H NMR (CDCl3, 300 MHz, -40 °C): 9.31 (4 H, d, J ) 6.4 Hz,
o-NC5H5), 7.93 (2 H, t, J ) 7.6 Hz, p-NC5H5), 7.49 (4 H, apparent t,
apparent J ) 7.0 Hz, m-NC5H5), 7.29 (3 H, m, o- and p-C6H5), 6.82 (2
H, m, m-C6H5), 6.74 (2 H, d, J ) 7.4 Hz, m-C6H3Me2), 6.50 (1 H, t,
J ) 7.4 Hz, p-C6H3Me2), 2.09 (6 H, s, C6H3Me2), -0.18 (9 H, s, SiMe3),
1
of 2,6-dimethylaniline at room temperature. The H NMR spectrum
after 6 d showed quantitative formation of 2 together with a new
resonance attributable to ButNH2.
NMR-Scale Reaction of [Ti(NBut){PhC(NSiMe3)2}Cl(py)2] (1)
with 2,6-Diisopropylaniline. A solution of 1 (6.6 mg, 0.011 mmol)
in CDCl3 (0.5 mL) in a 5 mm NMR tube was treated with ca. 1.2
(32) (a) Wedler, M.; Kno¨sel, F.; Noltemeyer, M.; Edelmann, F. T.; Behrens,
U. J. Organomet. Chem. 1990, 388, 21. (b) Boere´, R. T.; Oakley, R.
T.; Reed, R. W. J. Organomet. Chem. 1987, 331, 161.
(33) Hao, S.; Berno, P.; Minhas, R. K.; Gambarotta, S. Inorg. Chim. Acta
1996, 224, 37.
1
equiv of 2,6-diisopropylaniline at room temperature. The H NMR
spectrum after 6 d showed quantitative formation of 3 together with a
new resonance attributable to ButNH2.

3618 Inorganic Chemistry, Vol. 36, No. 17, 1997
Stewart et al.
[Ti2(µ-NBut)2{MeC(NC6H11)2}2Cl2] (4). A solution of Li[MeC-
(NC6H11)2]‚OEt2 (0.261 g, 0.86 mmol) in THF (20 mL) was added
over 10 min to a stirred solution of [Ti(NBut)Cl2(py)3] (0.368 g, 0.86
mmol) in THF at -60 °C. The resulting solution was allowed to warm
to room temperature and then stirred for 18 h. Volatiles were removed
under reduced pressure, the resulting orange residue was dissolved in
dichloromethane, and the mixture was filtered to remove LiCl.
Evaporation of the solvent and recrystallization from ether yielded red
crystals of 4, which were washed with cold ether (2 × 5 mL) and dried
in Vacuo. Yield: 0.166 g (51%).
Table 1. Crystallographic Data for
[Ti(N-2,6-C6H3Me2){PhC(NSiMe3)2}Cl(py)2] (2) and
[Ti2(µ-NBut)2{MeC(NC6H11)2}2Cl2] (4)
2
4
empirical formula
fw
temp/°C
wavelength/Å
space group
a/Å
C31H42ClN5Si2Ti
624.24
-53(1)
C36H68Cl2N6Ti2
751.66
-53(1)
0.710 73
P1h (No. 2)
11.219(5)
12.131(6)
13.208(7)
80.34(5)
87.41(4)
75.13(3)
1722.1(15)
2
1.20
0.417
0.054
0.056
0.710 73
P1h (No. 2)
10.455(3)
10.637(5)
11.024(3)
90.52(4)
112.62(3)
114.10(3)
1012.8(10)
1
1H NMR (CDCl3, 300 MHz, 25 °C): 4.68, 3.21 (2 × 2 H, 2 × m,
2 × NCHC5H10), 2.17 (6 H, s, overlapping 2 × MeCN2), 2.2-1.1 (40
H, series of multiplets corresponding to NCHC5H10 of two inequivalent
cyclohexyl rings), 1.19 (18 H, s, NBut). 13C{1H} NMR (CDCl3, 75.5
MHz, 25 °C): 178.9 (MeCN2), 73.7 (NCMe3), 59.9, 58.3 (2 ×
NCHC5H10), 34.0 (NCHC5H10), 31.0 (NCMe3), 26.6, 26.3, 26.2, 25.5
(some signals overlapping, NCHC5H10), 15.1 (overlapping 2 × MeCN2).
IR: 1735 (w), 1650 (m), 1495 (s), 1454 (vs), 1415 (s), 1360 (vs), 1258
(m), 1195 (vs), 1185 (vs), 1141 (w), 1075 (m), 1027 (w), 1003 (m),
937 (w), 892 (m), 819 (w), 802 (w), 791 (w), 768 (w), 745 (m), 722
(w), 634 (vs), 563 (w), 533 (m), 505 (m), 408 (s). Anal. Calcd (found)
for C36H68Cl2N6Ti2: C, 57.5 (58.1); H, 9.1 (8.8); N, 11.2 (11.5).
Variable-Temperature NMR Experiments for [Ti(NR){PhC-
(NSiMe3)2}Cl(py)2] [R ) But (1), 2,6-C6H3Me2 (2), 2,6-C6H3Pri2 (3)].
Detailed procedures for 2 only are given here by way of example.
Similar procedures were used for obtaining the corresponding rate and/
or equilibrium constants for 1 and 3.
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
Z
d(calcd)/Mg‚m-3
abs coeff/mm-1
R(Fo)a
1.23
0.550
0.0453
0.0495
Rw(Fo)b
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2
.
2
tropically. For compound 2, H atoms were placed in estimated positions
with C-H ) 0.96 Å and Uiso ) 1.3 × Uequiv or Uiso of the atom to
which each was bonded and were refined “riding” on their respective
supporting atoms. For compound 4, all H atoms could be located from
difference syntheses and were refined isotropically. For both structures,
examination of the refined secondary extinction parameter and |Fo| and
|Fc| for the strongest reflections and an agreement analysis suggested
that no extinction correction or weighting scheme needed to be applied.
All crystallographic calculations were performed using SIR9237 and
CRYSTALS-PC.38 Full listings of atomic coordinates, bond lengths
and angles, and thermal parameters have been deposited at the
Cambridge Crystallographic Data Centre. See also paragraph at end
of paper regarding Supporting Information.
A 0.05 mol‚dm-3 sample of [Ti(N-2,6-C6H3Me2){PhC(NSiMe3)2}-
Cl(py)2] (2) in CDCl3 was prepared in the drybox. NMR integration
yielded relative concentrations of 2, 2′, and free py at each temperature.
The relative concentrations were converted to absolute concentrations
by assuming that [2] + [2′] ) 0.05 mol‚dm-3 and that [py] ) [2′].
Kinetic parameters for the 2 f 2′ + py and 2′ + py f 2 processes
1
were obtained from five H NMR spectra of 2/2′ + py in the range
248 e T e 268 K in the intermediate-exchange regime. Lorentzian
curve fitting of the ortho methyl group resonances afforded ν1/2
(bandwidth at half-height) values from which were subtracted the
estimated natural line widths (1.8 Hz at 228 K) to give corrected ν1/2
values. The first-order (for 2 f 2′ + py) and pseudo-first-order rate
Results and Discussion
Although a variety of amidinate ligands of the general formula
RC(NR′)2 have been described in the literature,16,17 we were
particularly attracted by the N,N′-bis(trimethylsilyl)benzamidi-
nato [PhC(NSiMe3)2] and N,N′-bis(cyclohexyl)acetamidinato
[MeC(NC6H11)2] species because of the ease of preparation of
their lithium salts31-33 and the stabilizing properties they
generally impart to their metal complexes.
constants (for 2′ + py f 2) were calculated according to the expression
34
k ) πν1/2
.
The second-order rate constant k2′+pyf2 for 2′ + py f 2
was obtained from the pseudo-first-order rate constant (kobs) and [py]
at each temperature by assuming kobs ) k2′+pyf2[py]. Standard Eyring
plots afforded the activation parameters listed in Table 3 according to
standard procedures.35 Further measurements of [2], [2′], and [py] were
made in the range 228 e T e 243 K, but at these temperatures line-
broadening contributions from 2 f 2′ + py are less than or comparable
to the natural line width.
For 3, a lineshape analysis to obtain rate constants and activation
parameters was not possible due to the complex, overlapping multiplet
nature of the 1H resonances. For 1-3, equilibrium constants were
measured and plots of ln Keq Vs 1/T afforded ∆H and ∆S values. To
confirm that solvent effects are not significant, we found the equilibrium
∆H and ∆S (and hence the derived ∆G258) values in toluene-d8 solution
showed the same trends and as those found in CDCl3.
Crystal Structure Determination of [Ti(N-2,6-C6H3Me2){PhC-
(NSiMe3)2}Cl(py)2] (2) and [Ti2(µ-NBut)2{MeC(NC6H11)2}2Cl2] (4).
Crystal data collection and processing parameters are given in Table
1. Crystals were mounted in a film of RS3000 oil on a glass fiber and
transferred to a Stoe¨ Stadi-4 four-circle diffractometer equipped with
an Oxford Cryosystems low-temperature device.36 An absorption
correction based on ψ scans was applied to the data, and equivalent
reflections were merged. The structures were solved by direct methods
(SIR9237 ). Subsequent difference Fourier syntheses revealed the
positions of all other non-hydrogen atoms; these were refined aniso-
Reaction of Li[PhC(NSiMe3)2] with the complex [Ti(NBut)-
o
Cl2(py)3] at -40 C in THF gave the mono(N,N′-bis(trimeth-
ylsilyl)benzamidinato)titanium imido derivatives [Ti(NBut)-
{PhC(NSiMe3)2}Cl(py)2] (1) in 62% yield after standard workup
and recrystallization from hexane. Similarly the 2,6-disubsti-
tuted arylimido homologues [Ti(NAr){PhC(NSiMe3)2}Cl(py)2]
[Ar ) 2,6-C6H3Me2 (2), 2,6-C6H3Pri2 (3)] may also be prepared
by simple metathesis reactions. The red compounds 1-3 are
highly soluble in hydrocarbon solvents, and these solutions are
very air- and moisture-sensitive. A summary of the syntheses
and proposed structures for all the new compounds are shown
in Scheme 1; full characterization data are listed in the
Experimental Section.
Cooling of a hexane solution of [Ti(N-2,6-C6H3Me2){PhC-
(NSiMe3)2}Cl(py)2] (2) afforded X-ray-quality crystals. The
molecular structure of 2 is shown in Figure 1, and selected bond
lengths and angles are given in Table 2.
Compound 2 has a six-coordinate titanium(4+) center with
two mutually trans py ligands both bonded cis to the N-2,6-
C6H3Me2 and Cl moieties. The PhC(NSiMe3)2 ligand thus has
(34) Green, M. L. H.; Wong, L.-L.; Sella, A. Organometallics 1992, 11,
2660.
(35) Sandstro¨m, J. Dynamic NMR Spectroscopy; Academic Press: London,
1992.
(36) Cosier, J.; Glazer, A. M. J. Appl. Crystallogr. 1986, 19, 105.
(37) Altomare, A.; Cascarano, G.; Giacovazzo, G.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(38) Watkin, D. J.; Prout, C. K.; Carruthers, J. R.; Betteridge, P. W.
CRYSTALS-PC; Chemical Crystallography Laboratory, University of
Oxford: Oxford, U.K., 1996.

Titanium Imido Complexes
Inorganic Chemistry, Vol. 36, No. 17, 1997 3619
Scheme 1a
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
[Ti(N-2,6-C6H3Me2){PhC(NSiMe3)2}Cl(py)2] (2)
Ti(1)-Cl(1)
Ti(1)-N(1)
Ti(1)-N(2)
Ti(1)-N(3)
Ti(1)-N(4)
Ti(1)-N(5)
2.403(2)
1.727(4)
2.288(4)
2.114(4)
2.250(4)
2.247(4)
N(1)-C(1)
N(2)-Si(1)
N(2)-C(9)
N(3)-Si(2)
N(3)-C(9)
C(9)-C(10)
1.385(6)
1.737(4)
1.304(6)
1.760(4)
1.354(6)
1.501(6)
Cl(1)-Ti(1)-N(1)
Cl(1)-Ti(1)-N(2)
N(1)-Ti(1)-N(2)
Cl(1)-Ti(1)-N(3)
N(1)-Ti(1)-N(3)
N(2)-Ti(1)-N(3)
Cl(1)-Ti(1)-N(4)
N(1)-Ti(1)-N(4)
N(2)-Ti(1)-N(4)
N(3)-Ti(1)-N(4)
99.2(1)
91.2(1)
169.6(2)
152.8(1)
107.9(2)
61.7(1)
86.5(1)
93.3(2)
87.4(1)
94.2(1)
Cl(1)-Ti(1)-N(5)
N(1)-Ti(1)-N(5)
N(2)-Ti(1)-N(5)
N(3)-Ti(1)-N(5)
N(4)-Ti(1)-N(5)
Ti(1)-N(1)-C(1)
N(2)-C(9)-N(3)
N(2)-C(9)-C(10)
N(3)-C(9)-C(10)
89.3(1)
95.0(2)
84.9(1)
86.0(1)
171.2(2)
170.4(4)
116.7(4)
122.2(4)
120.9(4)
complexes [range 1.986(2)-2.177(2)
Å
for four ex-
amples],22,23,39,40 whereas the trans Ti-N bond length [Ti(1)-
N(2) ) 2.288(4) Å] appears to be relatively long. This
difference of 0.174(6) Å between the cis and trans bond lengths
in 2 is indicative of the well-known, strong trans influence of
multiply bonded ligands such as imido or oxo.1,10,41-43
a Reagents and conditions: (i) Li[PhC(NSiMe3)2] (1 equiv); THF;
18 h; for 1, 62%, for 2, 64%, and, for 3, 29%. (ii) Li[MeC(NC6H11)2]
(1 equiv); THF; 18 h, 51%.
NMR-scale reactions in CDCl3 show that complexes 2 and 3
are also accessible by reaction of 1 with the appropriate
arylamine. These imido exchange reactions are qualitatively
considerably slower than those reported previously for the [Ti-
(NBut)Cl2(py)3] system,9,10 requiring ca. 6 d to go to completion.
The room-temperature 1H and 13C NMR spectra of 1-3 are
broad, indicating that one or more fluxional processes take place
in solution. Examination of the variable-temperature NMR
spectra showed that the behaviors of the three complexes are
qualitatively the same, and so we shall discuss mainly the data
for [Ti(N-2,6-C6H3Me2){PhC(NSiMe3)2}Cl(py)2] (2) by way of
Figure 1. CAMERON57 plot of [Ti(N-2,6-C6H2Me2){PhC(NSiMe3)2}-
Cl(py)2] (2). Hydrogen atoms are omitted for clarity, and thermal
ellipsoids are drawn at the 20% probablility level.
one N donor atom cis [N(3)] and one approximately trans [N(2)]
to the imido nitrogen atom [N(1)]. The titanium-imido nitrogen
bond length in 2 [Ti(1)-N(1) ) 1.727(4) Å] is somewhat longer
than those in the six-coordinate arylimido complexes [Ti(N-4-
C6H4R)Cl2(py)3] [R ) H, TidN ) 1.714(2) Å; R ) Me, TidN
) 1.705(4) Å],9,10 possibly indicative of steric interactions
between the ortho-methyl of the arylimido ligand and the nearby
SiMe3 groups. In addition, the longer TidN bond length in 2
may also reflect a better net σ-donor ability of the PhC(NSiMe3)2
ligand as compared to the {Cl(py)} ligand set in [Ti(N-4-
C6H4R)Cl2(py)3], although this does not appear to result in a
significant lengthening of the Ti-Cl bond in 2. The cis (with
respect to the imido group) Ti-N(benzamidinate) [Ti(1)-N(3)
) 2.114(4) Å] bond length is similar to that found in other
inorganic and organometallic titanium(4+) PhC(NSiMe3)2
1
example. The variable-temperature H NMR spectra of 2 in
CDCl3 between 243 and 296 K are reproduced in Figure 2.
The NMR spectra of 2 are consistent with the temperature-
dependent, dynamic equilibrium between [Ti(N-2,6-C6H3Me2)-
(39) Fenske, D.; Hartmann, E.; Dehnicke, K. Z. Naturforsch. 1988, 43B,
1611.
(40) Sotoodeh, M.; Lechtweis, I.; Roesky, H. W.; Noltemeyer, M.; Schmidt,
H.-G. Chem. Ber. 1993, 126, 913.
(41) Lyne, P. D.; Mingos, D. M. P. J. Chem. Soc., Dalton Trans. 1995,
1635.
(42) Lyne, P. D.; Mingos, D. M. P. J. Organomet. Chem. 1994, 478, 141.
(43) Shustorovich, E. M.; Porai-Koshits, M. A.; Buslaev, Y. A. Coord.
Chem. ReV. 1975, 17, 1.

3620 Inorganic Chemistry, Vol. 36, No. 17, 1997
Stewart et al.
Table 3. Thermodynamic and Kinetic Parameters for the
Dissociative Equilibria of [Ti(NR){PhC(NSiMe3)2}Cl(py)2] [R )
But (1), 2,6-C6H3Me2 (2), 2,6-C6H3Pri2 (3)]a
Thermodynamic Parameters
R
∆H/kJ‚mol-1 ∆S/J‚mol-1‚K-1 ∆G258/kJ‚mol-1
But (1)
38.7 ( 1.5
47.3 ( 1.9
45.7 ( 2.0
108 ( 5
142 ( 5
172 ( 5
10.8 ( 2.8
10.7 ( 3.2
1.2 ( 3.3
2,6-C6H3Me2 (2)
2,6-C6H3Pri2 (3)
Kinetic Parameters
∆Hq/kJ‚mol-1 ∆Sq/J‚mol-1‚K-1 ∆Gq258/kJ‚mol-1
R ) But
1 f 1′ + py
1′ + py f 1
90.5 ( 3.4
39.3 ( 1.5
108 ( 7
-45 ( 3
62.5 ( 5.2
51.0 ( 2.3
R ) 2,6-C6H3Me2
2 f 2′ + py
2′ + py f 2
75.7 ( 2.9
21.3 ( 0.8
60 ( 4
60.3 ( 3.9
49.2 ( 2.6
-108 ( 7
a See text for further details.
N- and N′-SiMe3 groups as commonly observed for other
transition metal bis(trimethylsilyl)benzamidinates. The mech-
anism of SiMe3 group exchange is unknown, and both an in-
place rotation process and initial dissociation to a monodentate
PhC(NSiMe3)2 followed by a rearrangement process have been
considered as possibilities.26,44 Exchange between the SiMe3
groups in the bis(pyridine) complexes 1-3 is more easily
“frozen out”. This implies35 a greater steric hindrance to SiMe3
group exchange in the six-coordinate species, since the chemical
shift differences between the two SiMe3 1H NMR resonances
(of 3 and 3′) are comparable in the slow-exchange regime.
The signals attributable to 1-3 increase in intensity relative
to those of py and 1′-3′ as the temperature is lowered. Careful
integration of signal intensities for variable-temperature 1H NMR
spectra of solutions of [Ti(NR){PhC(NSiMe3)2}Cl(py)2] [R )
But (1), 2,6-C6H3Me2 (2), 2,6-C6H3Pri2 (3)] of known concentra-
tion afforded equilibrium constants (Keq) at different tempera-
tures. Table 3 lists the corresponding ∆S, ∆H, and ∆G258 values
extracted from plots of ln Keq Vs 1/T shown in Figure 3.
The general magnitude of the ∆G258 values (10.8 ( 2.8, 10.7
( 3.2, and 1.2 ( 3.3 kJ‚mol-1 for 1 f 1′ + py, 2 f 2′ + py,
and 3 f 3′ + py, respectively) shows that all three equilibria
are effectively thermochemically neutral. This results in part
from the large positive ∆S (also consistent with the dissociative
equilibrium as written), which nearly compensates for the
endothermic ∆H term as the temperature is increased. The
values of ∆H and ∆S in Table 3 are within the ranges previously
found for pyridine dissociation from first-row transition metal
complexes.45
Figure 2. Variable-temperature 300 MHz 1H NMR spectra for [Ti(N-
2,6-C6H3Me2){PhC(NSiMe3)2}Cl(py)2] (2) in CDCl3 in the range 243-
296 K. The sharp singlet at δ 7.26 ppm is due to residual CHCl3.
{PhC(NSiMe3)2}Cl(py)2] (2) and the mono(pyridine) adduct
[Ti(N-2,6-C6H3Me2){PhC(NSiMe3)2}Cl(py)] (2′) shown in
Scheme 1. At intermediate temperatures, the relative concentra-
tions of 2 and 2′ change with the amount of added pyridine in
a way that is consistent with the dissociative equilibrium
illustrated. The equilibrium constant associated with this process
is therefore defined as Keq ) [2′][py]/[2]. Furthermore, the line
widths of the ortho-methyl group resonances for 2 are inde-
pendent of added py, whereas those of 2′ broaden as py is added,
also consistent with the proposed equilibrium. At temperatures
below 260 K, the signals assigned to 2 are relatively sharp and
are consistent with the solid state structure. The remaining
signals are assignable to 2′ and free pyridine. The structures
proposed in Scheme 1 for 1′-3′ are the “least-motion” pos-
sibilities derived from 1-3. I.e., the titanium atom has a pseudo
trigonal bipyramidal geometry, with the imido nitrogen and one
benzamidinate nitrogen occupying the apical sites and the
remaining pyridine, chloride, and other benzamidinate nitrogen
lying in the equatorial plane. A square-based pyramidal
geometry with both benzaminate nitrogen atoms and the Cl and
py ligands cis to the imido ligand may also be possible.
However, because the diasterotopic methyl groups of the ortho-
isopropyl ring substituents in 3′ appear as a pair of doublets,
we can rule out an alternative pseudo trigonal bipyramidal
geometry (with the Cl or py ligand trans to the imido group),
since this would have a molecular mirror plane containing the
TidN(imido) vector.
The trends in ∆H, ∆S, and ∆G258 for 1-3 merit discussion.
The X-ray structures of homologous pairs of tert-butylimido
and arylimido complexes generally show that the former group
has a greater bond-lengthening (and, presumably, bond-weaken-
ing) effect on other ligands present.48,10,46-52 The values of ∆H
for 2 and 3 are comparable within error but are significantly
(44) Wedler, M.; Kno¨sel, F.; Edelmann, F. T.; Behrens, U. Chem. Ber.
1992, 125, 1313.
(45) Christensen, J. J.; Izatt, R. M. Handbook of metal ligand heats and
related thermodynamic quantities, 3rd ed.; Marcel Dekker: New York,
1983.
(46) Williams, D. N.; Mitchell, J. P.; Poole, A. D.; Siemeling, U.; Clegg,
W.; Hockless, D. C. R.; O’Neil, P. A.; Gibson, V. C. J. Chem. Soc.,
Dalton Trans. 1992, 739.
(47) Bell, A. Personal communication cited in ref 2.
(48) Clegg, W.; Errington, R. J. Acta Crystallogr., Sect. C 1987, 43, 2223.
(49) Stahl, K.; Weller, F.; Dehnicke, K.; Paetzold, P. Z. Anorg. Allg. Chem.
1986, 534, 93.
The 1H NMR SiMe3 resonances for 1′ and 2′ appear as broad
singlets which broaden further into the baseline in the low-
temperature spectra, and only for 3′ can two different SiMe3
resonances be resolved at low temperature. This fluxional
behavior is consistent with rapid exchange of the inequivalent
(50) Glueck, D. S.; Wu, J.; Hollander, F. J.; Bergman, R. G. J. Am. Chem.
Soc. 1991, 113, 2041.

Titanium Imido Complexes
Inorganic Chemistry, Vol. 36, No. 17, 1997 3621
Figure 4. CAMERON57 plot of [Ti2(µ-NBut)2{MeC(NC6H11)2}2Cl2]
(4). Hydrogen atoms are omitted for clarity, and thermal ellipsoids are
drawn at the 20% probablility level. Atoms carrying the suffix “B” are
related to their counterparts by the symmetry operator [2 - x, 1 - y,
1 - z].
coordinate or/and minimal preorganization of 2′ before pyridine
coordination occurs. The data for 1 show trends similar to those
for 2.
Figure 3. Plots of ln(Keq) Vs 1000/T for [Ti(NR){PhC(NSiMe3)2}Cl-
(py)2]. Key: NR ) NBut (1, b), N-2,6-C6H3Me2 (2, 4), N-2,6-C6H3-
Pri2 (3, O).
While this work was in progress, Hagadorn and Arnold
reported the bis(benzamidinato)titanium imido complexes [Ti-
(NSiMe3){PhC(NSiMe3)2}2]18 and [Ti(NBut){PhC(NSiMe3)2}2].53
We attempted to prepare bis(benzamidinato) imido derivatives
from our mono(benzamidinato) complexes but could not isolate
a pure product. The binuclear group 4 µ-imido amidinates [Ti2-
(µ-NPh)2{µ-HC(NPh)2}2{HC(NPh)2}2]19 and [Zr2(µ-NSiMe3)2-
(η2-PhCNSiMe3)2{PhC(NSiMe3)2}2]21 were also recently de-
scribed. So far in our studies, we have only found evidence
for mononuclear terminal titanium imido species when using
the N,N′-bis(trimethylsilyl)benzamidinate ligand.
We were also interested in preparing titanium imido com-
plexes supported by the N,N′-bis(cyclohexyl)acetamidinate
group so as to explore the effects of modifying the steric
requirements of the supporting amidinate ligand in these titanium
imido systems. Thus reaction of [Ti(NBut)Cl2(py)3] with 1
equiv of Li[MeC(NC6H11)2] in THF at -60 °C gave a color
change to dark orange after 18 h. Subsequent workup and
crystallization from diethyl ether afforded dark red crystals of
the binuclear complex [Ti2(µ-NBut)2{MeC(NC6H11)2}2Cl2] (4;
see Scheme 1) which were suitable for X-ray diffaction analysis.
The molecular structure of 4 is shown in Figure 4, and selected
bond lengths and angles are given in Table 4.
larger than that for 1. This would be consistent with the Ti-
pyridine bonds being slightly weaker in 1 than in 2 and 3,
although one cannot rule out nonbonded (steric) effects on the
enthalpy terms as the imido N-substituent is varied. Interest-
ingly, ∆S for the dissociation of pyridine from 1-3 increases
with the steric demands of the imido substituent. Indeed the
∆H values for 2 f 2′ + py and 3 f 3′ + py are very similar,
and so the ca. 60-fold difference in Keq at 258 K (and associated
ca. 10 kJ‚mol-1 difference in ∆G258) is mostly attributable to
entropy effects. We interpret the increase in ∆S from 1 f 1′
+ py to 3 f 3′ + py as reflecting increased steric hindrance to
internal rotation etc. in the six-coordinate complexes as com-
pared with that in the five-coordinate 1′-3′.
We have also extracted kinetic parameters for the dynamic
equilibria of 1 and 2. 1H NMR spectra of solutions of 1 and 2
with known concentrations were recorded at 5 K intervals
between 248 and 278 K and between 248 and 268 K,
respectively, in the intermediate-exchange regime. Standard
procedures (see Experimental Section) afforded the rate con-
stants for 1 f 1′ + py and 2 f 2′ + py (and for the reverse
processes, 1′ + py f 1 and 2′ + py f 2). Table 3 lists the
The solution 1H and 13C{1H} NMR data for 4 are consistent
with the solid state structure, which shows a crystallographically-
imposed centrosymmetric, binuclear geometry with five-
coordinate titanium centers, each possessing a terminal chloride
and N,N′-bis(cyclohexyl)acetamidinate ligand. The titanium
atoms are bridged by two tert-butylimido groups, each having
a trigonal planar nitrogen atom. A search of the Cambridge
Structural Database54,55 showed the geometry of the central {Ti2-
(µ-NBut)2} core in 4 to be similar to that found in a number of
other complexes (with a range of different terminal ligand types)
containing this fragment. There is a significant asymmetry in
the Ti-(µ-N) bond lengths of 4 [Ti(1)-N(1) ) 1.835(3) Å;
Ti(1)-N(1B) ) 1.997(3) Å]. The electronic origins of sub-
stantially asymmetric M-(µ-N) bond lengths in certain group
6 complexes possessing a central {M2(µ-NR)2} fragment have
corresponding ∆Sq, ∆Hq, and ∆Gq values extracted from
258
Eyring plots. For the purposes of discussion, we shall refer
only to the data for 2. The difference (ca. 11 kJ‚mol-1) between
the (activation) ∆Gq258 values for 2 f 2′ + py and for 2′ + py
f 2 compares well with the (thermodynamic) ∆G258 value of
10.7 ( 3.2 kJ‚mol-1 obtained from the equilibrium constants.
These results are consistent with a single transition state, and
the ∆Sq values imply dissociative and associative activation for
the 2 f 2′ + py and 2′ + py f 2 processes, respectively. The
activation enthalpy for py loss from 2 (∆Hq ) 75.7 ( 2.9
kJ‚mol-1) is substantially greater than that for py addition to 2′
(∆Hq ) 21.3 ( 0.8 kJ‚mol-1). This is consistent with early
Ti-py bond formation along the 2′ + py f 2 reaction
(51) Lewkebandra, T. S.; Sheridan, P. H.; Heeg, M. J.; Rheingold, A. L.;
Winter, C. H. Inorg. Chem. 1994, 33, 5879.
(52) Duchateau, R.; Williams, A. J.; Gambarotta, S.; Chiang, M. Y. Inorg.
Chem. 1991, 30, 4863.
(53) Unpublished results cited in ref 18.
(54) Allen, F. H.; Kennard, O. Chem. Des. Autom. News 1993, 8, 1, 31.
(55) Fletcher, D. A.; McMeeking, R. F.; Parkin, D. J. Chem. Inf. Comput.
Sci. 1996, 36, 746.

3622 Inorganic Chemistry, Vol. 36, No. 17, 1997
Stewart et al.
Table 4. Selected Bond Lengths (Å) and Angles (deg) for
[Ti2(µ-NBut)2{MeC(NC6H11)2}2Cl2] (4)a
N(1) and Ti(1)-N(1B) bond lengths in 4 mainly to steric effects
arising from the cyclohexyl rings lying somewhat asymmetri-
cally over the {Ti2(µ-NBut)2} unit.
The contrasting structures of [Ti(NR){PhC(NSiMe3)2}Cl-
(py)2] (1-3) and [Ti2(µ-NBut)2{MeC(NC6H11)2}Cl2] (4) show
the importance of the amidinate N-substituent in these systems.
We have also attemped to prepare (arylimido)titanium com-
plexes containing the N,N′-bis(cyclohexyl)acetamidinate ligand,
but these reactions have so far only provided complex,
inseparable mixtures.
Ti(1)‚‚‚Ti(1B)
Ti(1)-Cl(1)
Ti(1)-N(1)
Ti(1)-N(1B)
Ti(1)-N(2)
Ti(1)-N(3)
N(1)-C(1)
2.803(1)
2.321(1)
1.835(3)
1.997(3)
2.112(3)
2.076(3)
1.471(4)
N(2)-C(5)
N(2)-C(7)
N(3)-C(5)
N(3)-C(13)
C(5)-C(6)
Ti(1)-Cl(1)
1.332(5)
1.469(4)
1.330(4)
1.477(4)
1.502(5)
2.403(2)
Ti(1)‚‚‚Ti(1B)-Cl(1B) 108.66(4) N(1)-Ti(1)-N(2)
114.9(1)
138.8(2)
143.03(9)
106.7(1)
Ti(1)‚‚‚Ti(1B)-N(1B)
45.30(9) Ti(1)-N(1)-C(1)
Ti(1)‚‚‚Ti(1B)-N(2B) 154.95(9) Cl(1)-Ti(1)-N(3)
Ti(1)‚‚‚Ti(1B)-N(3B) 104.24(8) N(1)-Ti(1)-N(3)
Summary and Conclusions
Cl(1)-Ti(1)-N(1)
Cl(1)-Ti(1)-N(1B)
N(1)-Ti(1)-N(1B)
Cl(1)-Ti(1)-N(2)
108.31(9) N(1B) -Ti(1)-N(2) 152.2(1)
We have prepared and characterized some novel benzamidi-
nato- and acetamidinato-supported titanium imido complexes.
The solution dynamic equilibrium processes in the mononuclear
titanium imido complexes 1-3 have been fully analyzed and
show a substantial entropic contribution to the equilibrium
constants. We are currently exploring the reaction chemistry
of these and other early transition metal amidinates containing
metal-ligand multiple bonds.
99.24(8) N(1B) -Ti(1)-N(3) 94.7(1)
86.1(1) N(2)-Ti(1)-N(3)
91.41(9) Ti(1)-N(1)-Ti(1B) 93.9(1)
62.9(1)
a Atoms carrying the suffix “B” are related to their counterparts by
the symmetry operator [2 - x, 1 - y, 1 - z].
been discussed in detail previously by Nugent and co-workers.56
These researchers suggested that a substantial distortion of the
M-(µ-N) bond lengths in four-coordinate group 4 {M2(µ-
NR)2}-containing complexes, however, is not expected on
electronic grounds. Our interpretation of Nugent and co-
workers’ theoretical model suggests that fiVe-coordinate com-
plexes having a geometry of the type shown by 4 should also
be free of such distortionssaccording to electronic arguments
at least. We therefore attribute the difference in the Ti(1)-
Acknowledgment. This work was supported by grants (to
P.M.) from the EPSRC, Leverhulme Trust, and Royal Society.
We thank the EPSRC for a studentship (to P.J.S.) and the
provision of an X-ray diffractometer. We acknowledge the use
of the EPSRC Chemical Database Service at Daresbury Labora-
tory.
Supporting Information Available: Eyring plots for 1 and 2 and
ln Keq Vs 1/T plots for 1-3 (7 pages). X-ray crystallographic files, in
CIF format, for 2 and 4 are available on the Internet only. Ordering
and access information is given on any current masthead page.
(56) Thorn, D. L.; Nugent, W. A.; Harlow, R. L. J. Am. Chem. Soc. 1981,
103, 357.
(57) Watkin, D. J.; Prout, C. K.; Pearce, L. J. CAMERON; Chemical
Crystallography Laboratory, University of Oxford: Oxford, U.K.,
1996.
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